As is well known, a circuit breaker is an automatically operated electro-mechanical device designed to protect a conductor from damage caused by a power overload or a short circuit. Circuit breakers may also be utilized to protect loads. A circuit breaker may be tripped by an overload or short circuit causing an interruption of power to the load. A circuit breaker can be reset (either manually or automatically) to resume power flow to the loads. One type of circuit breaker that provides instantaneous short circuit protection to motoros and/or motor control centers (“MCC”) is called a motor circuit protector (MCP). A typical MCP includes a temperature-triggered overload relay, a circuit breaker, and a contactor. An MCP circuit breaker must meet National Electric Code (“NEC”) requirements when installed as part of a UL-listed MCC to provide instantaneous overload protection.
Mechanical circuit breakers energize an electro-magnetic device such as a solenoid to trip a breaker instantaneously due to large surges in current such as by a short circuit. The solenoid is tripped when current exceeds a certain threshold. MCPs must protect against fault currents while avoiding tripping on in-rush motor currents or locked-rotor currents, but these current levels vary by motor. Existing MCPs have a relatively limited operating range, so they are suitable for protecting motor circuits within the MCP's operating range. For motor circuits outside of a particular MCP's operating range, a different MCP must be designed for the operating parameters of those motor circuits.
It is costly to design a different MCP device for different current ratings, and it is also costly to inventory and distribute many different MCP devices. What is needed is an MCP device with user-adjustable and automatically configurable trip point settings over a broad range of current ratings. What is also needed is a circuit protection device that couples a mechanical button and a potentiometer for adjusting trip levels of an electrical circuit.